Isotonic IV Solutions

(Here’s where you can read an UPDATED VERSION of this article about Isotonic Solution)

If you’re looking for a list of IV solutions to memorize, then you’re in the wrong place.

But if you want to understand WHY and HOW IV solutions work the way that they do so that you can become a better nurse…here you go!

If you haven’t already seen the results of my osmosis experiment from last week, make sure to check that out, because I’ll be referring to it in all of my posts this week.

In a healthcare setting, Isotonic solutions are ubiquitous (that means they’re everywhere).  The definition of “isotonic” for the purposes of nursing is any solution that has approximately the same ratio of solute to solvent that you see in blood.

The most obvious one is 0.9% Saline Solution, better known as Normal Saline.  Normal Saline is given to increase the amount of fluid in the blood vessels (intravascular space), without significantly changing the balance of electrolytes in the body.  This is useful for making sure a patient remains in a well-hydrated state of homeostasis.  Normal Saline also happens to be the only IV solution that can be infused at the same time as a blood product.

I recently observed the dramatic results that Normal Saline can produce.  After I finished recording my Osmosis Experiment, I was curious to find out if the shrunken state of my severely dehydrated egg could be reversed.  So I plunked it into my Normal Saline Solution and waited to find the answer.  It only took a few short hours to discover that the Isotonic Solution easily rehydrated my shriveled egg until it looked like this:

Needless to say, I was as giddy as a school girl!  (As I’ve already mentioned in previous posts…yes, I realize that I am a big nerd :))  I was actually surprised by how quickly the osmosis reaction happened to refill the egg with water, although I suppose I shouldn’t have been.  Isotonic solutions can work pretty quickly in the body, too, to reverse similar problems. Once the egg was rehydrated, I couldn’t tell it apart from the other eggs in my osmosis experiment.

There’s some other Isotonic Solutions that you should be familiar with, too:

• 0.9% Saline (aka Normal Saline)
• Ringer’s Solution
• Lactated Ringers
• 5% Dextrose in 0.225% Saline
• 5% Dextrose in Water (technically, Isotonic, but physiology hypotonic…I’ll explain in a minute)

Ringer’s and Lactated Ringer’s Solutions contain a wider variety of electrolytes than Normal Saline, which makes them even more similar to what’s found in blood plasma.  Normal Saline only includes Sodium and Choride (Na⁺ and Cl^–).

Quick side note I want to point out:  even though Normal Saline doesn’t contain ALL of the electrolytes found in the blood stream, Sodium and Chloride are by far the most common, which is what makes Normal Saline work so well as an isotonic solution.  To help you remember that, just think about the normal ranges for each electrolyte…sodium and chloride have the biggest normal values (135-145 mEq/L and 96-106 mEq/L, respectively)!

The Isotonic Dextrose solutions have the same goal as the hypertonic Dextrose solutions:  to provide extra calories to the patient.  Remember, Dextrose is just a sugar, which can be easily absorbed by the body and turned into energy.  5% Dextrose in Water is a special case, though.  Although it is technically isotonic, it acts upon the body as if it is hypotonic. The reason is because once the dextrose has been absorbed, there is only plain water left.  Obviously, plain water without anything in it is hypotonic!  So you’ll end up with the same effects that you would see if you had given the patient a Hypotonic IV solution to begin with.

I hope this gives you a better understanding of isotonic IV solutions.  Please leave a comment below to share one new thing that you learned about isotonic solutions!

Nicole Whitworth

Nicole is a Professional Nursing Tutor with over 15 years experience, and the founder of Your Nursing Tutor. She has a BSN, and an MA in Clinical Psychology. Nicole specializes in providing easy-to-follow, proven study methods (like the Silver Bullet Study System) that transform frustrated nursing students into calm, confident nurses! When she’s not helping students through her Live Tutoring Membership, Nicole loves spending time with her husband, homeschooling their 6 kids, and staring at sunflowers.